H-068. The Escherichia coli sRNAs CsrB and CsrC Are Strongly Induced during Growth in Nutrient Poor Medium

K. Jonas1,2, O. Melefors1,2;
1Karolinska Inst., Stockholm, SWEDEN, 2Swedish Inst. for Infectious Disease Control, Solna, SWEDEN.

Background: An increasing number of small RNAs (sRNAs) has been shown to regulate critical pathways in pro- and eukaryotes. However, the environmental conditions, triggering the expression of sRNAs, are in many cases still unknown. This study aimed at the identification of environmental conditions, controlling the expression of the two Escherichia coli sRNAs CsrB and CsrC, both acting as antagonists of the global carbon storage regulator protein (CsrA). Methods: csrB, csrC and csrA expression was measured under various growth conditions by quantitative Real-Time PCR or beta-galactosidase assays with chromosomal lacZ fusions. CsrA protein levels were determined by Western Blot analysis. Results: Expression of csrB and csrC was strongly increased in a culture grown in minimal medium compared to a culture grown in rich medium. The level of CsrA didn’t vary between the different media. csrB and csrC expression was strongest when acetate or succinate were the sole carbon sources in the medium, but lowest when glucose was the sole carbon source. Addition of concentrated rich medium or a mixture of all 20 amino acids to a growing culture in minimal medium led to a clear reduction in the CsrB and CsrC levels within ten minutes. This indicates that the availability of amino acids, which are preferentially consumed by Escherichia coli in rich medium, has a repressing effect on csrB and csrC expression. By using different genetic mutants we found that the elevated expression of csrB and csrC in minimal medium greatly depends on the phosphorylation activity of the BarA-UvrY two-component system, which has previously been demonstrated to control csrB and csrC transcription in rich medium. Conclusions: Our findings let suggest that csrB and csrC expression is controlled by the nutrient availability of the medium. We propose that the sensor BarA mediates this response by either sensing the presence or absence of a compound in the medium or by sensing the metabolic status of the cell by an indirect mechanism.

169/H. Transcription Control

Tuesday, 1:00 pm | Poster Hall